Method of and apparatus for purifying polluted gases

ABSTRACT

A method and apparatus for ultrasonically generating fog with a venturi having a converging section, a diverging section and an intermediate restricted throat section through which extends a slot for substantially the entire width thereof and in a plane substantially transverse to the axis thereof. Concurrently water is fed through the throat slot to form a continuously flowing thin sheet of water across the width of the throat section while gas under pressure is fed into the converging section of the venturi wherein the gas is formed into a stream. The gas stream is then fed into the throat section to increase its linear velocity to produce a sound wave which, together with the gas under pressure, moves through said sheet of water flowing across the width of said throat section continually, breaking the sheet of water into fine water droplets having vibrating surfaces. The comingled gas under pressure and the water droplets are then expanded in the venturi divergent section and pass therefrom as ultrasonically generated fog with fine vibrating droplets of water.

nited States Patent Eng et al.

[ 51 Feb. 22, 1972 [54] METHOD OF AND APPARATUS FOR PURIFYING POLLUTEDGASES [72] Inventors: Joseph W. Eng, Bayside, N.Y.; Stanley C.

F. Lin, Matawan, NJ. [73] Assignee: Lin Eng Corporation, New York, NY.

[22] Filed: Sept. 12, 1969 [21] App1.No.: 870,780

Related US. Application Data [62], Division of Ser. No. 664,416, Aug.30, 1967, Pat.

[52] U.S.Cl ..116/137, 55/8,239/434, 252/359 A [51] Int. Cl ..B06b 3/00[58] Field of Search ..ll6/ll2,117, l37',252/359.1; 55/815; 239/426,434, 102, 543

[56] References Cited UNITED STATES PATENTS 498,591 5/1893 Vollmer etal. ..239/434 1,592,982 7/1926 Loepsinger ...,239/434 X 1,784,50312/1930 Swann ....239/434 X 2,559,864 7/1951 Firth ..116/137 2,676,4714/1954 Pierce, Jr ..239/434 X Primary ExaminerLouis J CapoziAttorney-Morgan, Finnegan, Durham & Pine [5 7] ABSTRACT A method andapparatus for ultrasonically generating fog with a venturi having aconverging section, a diverging section and an intermediate restrictedthroat section through which extends a slot for substantially the entirewidth thereof and in a plane substantially transverse to the axisthereof. Concurrently water is fed through the throat slot to form acontinuously flowing thin sheet of water across the width of the throatsection while gas under pressure is fed into the converging section ofthe venturi wherein the gas is formed into a stream. The gas stream isthen fed into the throat section to increase its linear velocity toproduce a sound wave which, together with the gas under pressure, movesthrough said sheet of water flowing across the width of said throatsection continually, breaking the sheet of water into fine waterdroplets having vibrating surfaces. The comingled gas under pressure andthe water droplets are then expanded in the venturi divergent sectionand pass therefrom as ultrasonically generated fog with fine vibratingdroplets of water.

4 Claims, 1 1 Drawing Figures PAIENTEUFEB22 I972 SHEET 1 BF 8 INVIQIJ'I'URS JOSEPH W. ENG STANLEY C. F, LIN

1 .1 0 n a M wwp wr o uw 3. a U 2 MORGAN, FINNEGAN. DURHAM 8| PINEATTORNEYS PAIENTEUFEBZZ m2 1 3. 643.623

saw 2 BF 8 FIG? lNVhf/IURS v JOSEPH w. ENG

STANLEY C. F. LIN BY MORGAN, FINNEGAN, DURHAM 8 PINE ATTORNEYSPAIENTEUFEBZZ |912 I 3, 643.623

sum 3 [1F 8 FIG 3 nfvmrmns JOSEPH W. ENG STANLEY C. F. LIN

BY MORGAN, FINNEGAN.,DURHAM 8| PINE ATTORNEYS PATENTEUFEB 22 m2 3,643.62 3

sum 4 or s FIG-5 lNVizf/TURS JOSEPH w. ENG STANLEY c. F. LIN

BY MORGAN, FINNEGAN. DURHAM 8| PINE ATTORNEYS PAIENI0FB22 I972 3.643.623

sum 5 or 8 INVLNTORS.

JOSEPH w. ENG STANLEY c. F. LIN

MORGAN, FINNEGAN, DURHAM 8| PINE ATTORNEYS PAIENIEUFEB22 I972 3. 643,623

SHEET 6 OF 8 FIG"8 LOW #202 FREQUENCY OSCILLATOR VOLTAGE 204 CONTROLLEDOSCILLATOR SILICON 2/2 D C CONTROLLED RECTIFIER SUPPLY GATED VOLTAGECONTROLLER 2/0\ "20.8 2533 WINDING ARMATURE INVENTORS JOSEPH Wv ENGSTANLEY C-F. LIN BY MORGAN, FINNEGAN, DURHAM a PIN:

ATTORNEYS PATENTEDFEBZZIQTZ 3.643.623

sum 7 OF 8 336 338 W. FIG- IO 33a INVIzIJIORS JOSEPH w we STANLEY C. FLIN BY MORGAN, FINNEGAN, DURHAM 8x PINE ATTORNEYS PAIENTEUFEB22 1972SHEET 8 BF 8 fo 8 0 4 4 5 H 5 4 4 4 Z 3 4 M I r 4 4) S R R f S A R R m mR W YL G Tm E L MA LA U. h W 0 N ER W A E N WHIII' WII' MII M I L II M WL A W M L M C Q0 F O E C A A C C D 5 4 s v 4 R R u w E m j m E WR TTc TA F A0 AHR A R I IIRS 2 I- M s w S w W A W M M c T 9 4 4 a M 4 6 m 4 m AP 0 MN [MM 4, m E 4 M W m INVh'NTORS "I I JOSEPH w. ENG

BY STANLEY c. F LIN MORGAN, FINNEGAN, DURHAM 8 PINE ATTORNEYS METHOD OFAND APPARATUS FOR PURIFYING POLLUTED GASES This application is adivisional of our copending application,-

Ser. No. 664,416, filed Aug. 30, 1967 now US. Pat. No. 3,494,099.

A This invention relates to a method of and apparatus for removingcontaminants from polluted gases with a low flow resistant, porous,infinite capacity filter in which ultrasonically generated, oscillatingfog of substantially increased contact area and contact duration,contacts, absorbs and agglomerates contaminants carried by such gases,and from which the absorbed agglomerated contaminants are removed.Preferably the fog droplets are charged electrically and activatedchemically, as well as generated in a range of sizes best suited forremoving contaminants from the polluted gases.

This invention also relates to a method of and apparatus for removingcontaminants from the polluted gases by passing such gases throughultrasonically generated fog, at least some of which is frequentlymodulated. In accordance with this invention, such fog is provideddownstream of said filter, and the polluted gases are passed throughsuch fog before entering said filter.

Pollution of environments inhabited by human, animal or plant life is ofgrave and growing public concern. The discharge of carbon particles andsulphur and carbon gases into the atmosphere from heat, power and wastedisposal combustion processes is a prime example of pollution upon whicha good deal of this concern is focused.

l-leretofore, efforts to remove solid and gaseous contaminants fromgaseous streams, such as the exhaust or waste from industrially producedflue streams, with fresh water sprays, dry electrostatic percipitators,and cyclone separators have been generally unsatisfactory.

For example, high chimney structures are unsatisfactory, not onlybecause of increased costs, but because of the contaminants which arestill ultimately discharged into the atmosphere.

ln addition, while presently available techniques are sup posed toremove large or coarse solid particles present in contaminated gaseousstreams, no provisions are made for effectively removing small micronand submicron sized solid particles. Accordingly, flue streams commonlycarry fine injurious solid particles into atmosphere. Furthermore, suchtechniques commonly do not provide for the removal of undesirable gasesfrom the contaminated streams, so that along with the fine particlescarried by flue streams, carbon and sulphur gases are also exhausted toatmosphere.

Furthermore, efficient, low-flow, resistant equipment which can beinstalled within gaseous discharging conduits, such as chimney stacks,has heretofore not been generally available. Rather, only separatelyinstalled costly and cumbersome systems are available which do notefficiently remove solid and gaseous contaminants from streams beingexhausted to atmosphere.

It is one object of this invention to provide a new and improved methodof and apparatus for eliminating pollution of environments inhabited byhuman, animal and plant life by efficiently removing contaminants fromgaseous streams discharging or exhausting into such environments withoutundue installation and operating expenses.

Another object of this invention is to provide a new and improved methodof and apparatus for removing atmospheric contaminants from gaseousstreams within available equipment for exhausting or discharging suchstreams to atmosphere.

A further object of this invention is to provide a new and improvedmethod of and apparatus for removing atmospheric contaminants whicheliminates the need for the present high chimney structures.

Another object of the invention is to provide a filter of large surfacearea, deep filtering length, and an unlimited filtering capacity forremoving contaminants contained in gaseous streams.

Still another object of this invention is to remove contaminants frompolluted gases by passing such gases through a low flow resistant,porous, infinite capacity filter, in which ultrasonically generated,oscillating fog absorbs and agglomerates contaminants, and from whichthe absorbed and agglomerated contaminants are removed.

Another object of this invention is to generate contaminant removing fogthat is ultrasonically generated to provide vibrating fog droplets andto three dimensionally oscillate such fog droplets to provide increasedcontact area and contact duration between the polluted gases and thefog.

A further object of this invention is to provide ultrasonicallygenerated fog of liquid droplets composed of a range of sizes forwetting, absorbing and agglomerating a range of micron sized particlescarried by a polluted gas.

Still another. object of this invention is to provide within anindustrial chimney stack an infinite capacity filter and afrequency-modulated ultrasonic fog generator to remove solid particlesand carbon and sulphur-gases from a flue stream being exhausted toatmosphere.

Another object of this invention is to provide the frequencymodulatedultrasonic fog generator and one or more large capacity fog generatorswithin the chimney stack downstream of the infinite capacity filter tofurther facilitate removal of contaminants from the flue stream.

A further object of this invention is to provide automatically operatedmeans for controlling the flow of polluted gases through the contaminantremoving apparatus of the invention and for controlling the liquid usedby such apparatus for removing the contaminants.

In accordance with the present invention, solid and gaseous contaminantsare removed from polluted gases by a filter of low-flow resistance, oflarge surface area, of substantial depth, and of infinite filteringcapacity, and in which vibrating and oscillating liquid dropletscontact, absorb and agglomerate gases and solid contaminants in thepolluted gases, and from which agglomerated solids and agglomeratedcontaminant containing liquid formed from the droplets are continuouslyremoved. An ultrasonic generator is provided within the filter thatproduces the vibrating droplets in the form of fog which has substantialheight and depth and which continuously moves across said filter. At thesame time an electric field and a sound wave are generated within thezone substantially perpendicular to and through the moving fog to causethree dimensional oscillatory motion of the vibrating fog droplets. Theoscillation of. the moving, vibrating fog droplets in multidirectionsincreases many fold the contact area of the fog droplets and the contactduration between fog droplets and polluted gases. Thus, with increasedcontact area and contact time the liquid droplets are extremelyeffective in removing contaminants from polluted gases.

Furthermore, the ultrasonic generation of the fog is preferablyfrequency modulated to provide fog droplets having a range of micronsizes best suited to absorb and agglomerate the range of sizes of thesolid contaminant generally carried by these polluted gases. Inaddition, the fog droplets are preferably charged electrically toincrease their absorbing and agglomerating capacity of both solid andgaseous contaminants.

Also, in accordance with the present invention, all or essentially allof the contaminants can be removed from polluted gases, particularly hotpolluted gases exhausted from industriall processes, in successivestages or zones through which the polluted gases are passed before beingexhausted into the atmosphere.

Briefly the polluted gases are initially passed through a first zone inwhich the large solid particles are scrubbed therefrom while the finesolid particles are wetted and material amounts of gaseous contaminantsare absorbed. in one embodiment the scrubbing, wetting and absorbing isaccomplished by fog composed of vibrating droplets produced by one ormore large capacity ultrasonic fog generators, the number of whichrelates to the volume of polluted gases and the degree of pollutionthereof. In another embodiment the fog in the first zone is generated inone of other zones and moves into said first zone.

In a second zone, the scrubbed polluted gases are passed throughfrequency-modulated ultrasonically generated fog wherein vibrating fogdroplets are produced in a range of sizes best suited to agglomerate andcause removal of the range of sizes of solid particles still carried bythe polluted gases. In this zone further amounts of the contaminatinggases are also removed.

In a successive zone, and preferably the final zone, all or essentiallyall of the remaining contaminants are removed by the infinite capacityfilter of the present invention. Removal of the contaminants from thepolluted gases from this zone, as well as other zones of thisembodiment, is accomplished by the forces of gravity acting upon theagglomerated solid particles and the contaminant containing agglomeratedliquid droplets.

The liquid used in generating the fog of the present invention iscapable of wetting, absorbing and agglomerating the contaminantscontained or carried by a polluted gas. Water, for these reasons, aswell as for the availability and inexpensiveness, is preferred. Wherewater is used in generating the fog and where the polluted gases containsulphur gases, moreover, the absorbed sulphur gases form with the waterdilute sulphuric acid which is collected, cleaned and recycled back intothe process to form chemically activated fog capable of absorbingadditional quantities of gaseous contaminants.

In one embodiment of the apparatus of the invention, the filtercomprises a frequency-modulated ultrasonic fog generator positionedwithin the filter which produces a continuous, moving, deep blanket offog across the filter that contains a range of droplet sizes, such asfrom about 1 to 100 microns. For threedimensional oscillation of the fogthe filter includes two spaced, relatively stationary, porous gridsorelectrodes positioned to produce a strong electrical fieldsubstantially perpendicular to the generated fog, and an intermediategrid or electrode positioned to produce vibrations and a sound wave alsosubstantially perpendicular to the generated fog. The electric field isproduced between the outer grids by a first circuit means which appliesan alternating, high-voltage potential between the outer grids. At thesame time a second circuit means applies a fixed potential to theintermediate grid. The alternating attraction of the intermediate gridto one outer grid and then the other causes the intermediate grid tovibrate and generate a sound wave.

In one embodiment, the frequency-modulated ultrasonic fog generator ofthe invention uniformly and laterally dispenses fog composed of a rangeof fine, vibrating, water droplets for optimum wetting, absorbing, andagglomerating the range of solid particles commonly carried by pollutedgases. Such fog generator includes a sound generator which laterallygenerates sound waves of variable frequency along with laterallydischarging air under pressure. At the same time, water means provide anannular stream about .the sound generator through which the sound wavesand air under pressure move breaking the stream of water into finevibrating droplets and carrying such droplets in the form of foglaterally outwardly. And control means vary the frequency of the soundgenerator to break the water droplets into the desired range of sizesfor removing the different sizes of solid contaminants.

The large capacity ultrasonic fog generator of the present inventioncomprises a venturi having a converging section into which gas underpressure, such as air, if fed, a diverging section from which fogcomposed of vibrating liquid droplets carried by air under pressuredischarged, and an intermediate throat having a slot thereacross throughwhich liquid, such as water, is fed to form a continually flowing sheetof water across the throat. At the same time the air under pressure isformed into a converging airstream and fed into the throat above theslot, wherein the linear velocity of the airstream is increased toeffect a sound wave. Such sound wave and the airstream then drivesthrough the sheet. of water flowing across the slot and continuallybreaks it up into finer water droplets with vibrating surfaces. Finallythe commingled air under pressure and the fine water droplets areexpanded in a controlled manner through the diverging section and flaredtherefrom into ultrasonically generated fog.

In accordance with the present invention, the method of and apparatusfor removing contaminants from polluted gases can be embodied inavailable equipment for exhausting or discharging such gases toatmosphere, such as chimney stacks. Furthermore, such stacks containingthe contaminant removing apparatus of the present invention can be ofsubstantially less height then presently used because all or essentiallyall of the contaminants are removed from the polluted gases before beingdischarged into atmosphere within the lower segment of the stack.

To insure suitable flow of the polluted gases, such as through chimneystacks, and the removal of contaminants from such gases, the presentinvention also includes automatically controlled air blowing means thatinduces the flow of the polluted gases, as well as automatic controlmeans operatively connected to the liquid supply means for controllingthe supply of liquid in relation to the temperature and smoke density ofthe polluted gases.

The foregoing and other objects may be understood more fully from thefollowing specification which sets forth an illustrative embodiment ofthe invention. Although an invention is described principally inconnection for removal of contaminants from hot polluted flue gases, theinvention is nevertheless applicable for removing contaminants frompolluted gases produced by other sources.

The drawings which are part of the specification consist of thefollowing:

FIG. 1 is a side elevational view, partly sectional and partlyschematic, of a stack for a steam-generating furnace containing oneembodiment of the invention for removing contaminants from a flue streambeing exhausted to atmosphere through the stack;

FIG. 2 is a longitudinal, sectional view of one embodiment of the largecapacity ultrasonic fog generator of the invention, several of which aresuspended in the lower end of the stack in the zone designated in FIG. 1as zone A;

FIG. 3 is a side elevational view of one embodiment of thefrequency-modulated ultrasonic fog generator of the invention, one ofwhich is suspended in the stack in the zone designated 8, and anotherone of which is suspended in the filter designated zone C, as shown inFIG. 1:

FIG. 4 is a plan view of the frequency-modulated ultrasonic foggenerator of FIG. 3;

FIG. 5 is a longitudinal cross-sectional view of FIG. 3;

FIG. 6 is a side elevational view, partly in section, of the perforatedsound-generating ring housed in the frequency-modulated ultrasonic foggenerator as shown in FIG. 5;

FIG. 7 is a plan view of the sound-generating ring of FIG. 6;

FIG. 8 is a block diagram of the variable-speed motor control of thefrequency-modulated ultrasonic fog generator shown in FIG. 5;

FIG. 9 is a side elevational view, partly schematic and partlyperspective, of one embodiment of the filter of the invention having afrequency-modulated ultrasonic fog generator and electrically operatedsound-producing vibrator suspended in the stack in the zone designatedC, together with a schematic wiring diagram of the circuit for producingsaid vibrations;

FIG. 10 is a graphic representation of the high-voltage alternatingpotential applied to the outer screen-type grids of the filter relativeto the potential applied to the vibrator; and

FIG. 11 is a block diagram of the smoke and temperaturesensing liquidflow control system for the apparatus of the invention within the stackas schematically shown in FIG. 1.

Referring to FIG. 1 there is shown a vertically extending stack 10having a base 12, and a cylindrical wall 14 extending upwardly therefromforming a passage 16 connected at the lower end 18 to a flue 20 forcarrying hot polluted gases from one or more steam-generating furnaces,chemical-processing equipment, or industrial burners, and open at itsupper end 22 for discharging a purified flue stream to atmosphere.

The contaminants carried by the flue stream into the stack essentiallyconsist of solid carbon particles of submicron and micron sizes andsulphur and carbon gases. Within the stack passage 16 between such ends18 and 22 is one embodiment of the apparatus for removing contaminantsfrom the hot polluted gaseous stream.

In removing contaminants from the flue stream water is used whichbecomes activated by the absorbed sulphur gases to thereby form asolution of dilute sulphuric acid with increased absorbing capabilities.In this embodiment of the invention, the activated water is collected atthe base 12 of the stack 10 along with solid particles removed from theflue stream, drained through a conduit 26 connected into the base 12 anda reservoir 28 where the particles are separated from the activatedwater. The cleansed activated water, with fresh makeup water added asrequired, is then recycled back into the process through a supplyconduit 30. Simultaneously, air under pressure is fed from a sourcethrough a supply conduit 32 to the apparatus within the stack 10 whichgenerates activated fog that removes the contaminants carried by theflue stream as will be presently explained.

Within the stack, contaminants are removed from the upwardly flowingflue stream in three superimposed vertical zones: zone A, zone B andzone C. These zones extend across the stack passage 16 and arecompletely open to one another so that there is some overlap in theactions of the zones.

Zone A forms the lowermost contaminant removing area and is positionedabove the stack base 12 so that the hot polluted gases from flue aredischarged directly thereinto. In the upper portion of zone A for thisillustration are three large capacity ultrasonic fog generators 34suspended in spaced relationship for providing a fog across the stackpassage 16 composed of fine vibrating chemically activated droplets as auniform curtain through the upwardly counterflowing hot polluted gasesdischarged into the stack 10 as shown in FIG. 1. In zone A large solidcarbon particles are scrubbed from the flue gas stream while the finersolid carbon particles are wetted for further processing. Furthermore,material amounts of the sulphur and carbon gases are absorbed by thevibrating chemically activated water droplets. The scrubbed particlesand agglomerated containing droplets are removed by gravity collectingat the stack opening 24 for removal through the drain conduit 26.

In addition, the fog cools the temperature of the hot flue stream whilesuch stream, in turn, thermally breaks the fine water droplets intostill smaller sizes by converting them to steam. The steam so generatedincreases the absorbing and wetting effectiveness of droplets. With thetemperature of the flue stream reduced, moreover, the velocity thereofalso decreases, thereby providing additional time for scrubbing withinzone A.

For generating the ultrasonic dispensed fog both compressed air andwater are simultaneously fed to and through each of the generators. Asschematically shown in FIG. 1, the water containing dilute sulphuricacid is fed from the supply conduit to a feed conduit 36 connected in aseries to the generators 34. At the same time compressed air is fed fromthe supply conduit 32 to a feed conduit 38 also connected in series tosuch generators 34.

Each ultrasonic generator 34 produces large quantities of fog bycomprising a hollow vertically positioned cylindrical housing 40 havinga cylindrical shell 42 threaded at both ends to receive correspondinglythreaded closure caps 44 and 46 as shown in FIG. 2. Extending throughthe central portion of the shell 42 and the top cap 44 are bores 48 and50 into which are welded inlet nipples 52 and 54 for the water and airfeed conduits 36 and 38, respectively, shown in FIG. 1. The bottom cap46 includes an opening 56 therethrough having an inner annular portion58 and a contiguous outer flared portion 60 communicating with thesurrounding environment of the stack 10.

Vertically positioned within the housing-40 is a venturi 62 havingspaced annular flanges 64, 66, 68 and 70, to slidably guide and positionthe venturi 62 within the cylindrical housing 40, and divide housinginterior into three compartments 72, 74 and 76, with the middlecompartment 74 communicating with the water inlet 52. The venture 62consists of two parts. The upper portion 78 of the venturi 62 consistsof an inlet section 79 of'uniform diameter which communicates with theair inlet 54, a converging section 80, and a segment 82 of a throatwhich is positioned in the middle compartment 74. The lower portion 84of the venturi 62 consists of the other segment 86 of the throat spacedfrom the upper segment 82 to form a slot 88 thereacross adjustablyopened to the middle compartment 74, and a diverging section 90 havingan inside diameter at the outlet equal to the annular portion 58 of theopening 56 in the bottom cap 46. Sealing gaskets 92 with centralopenings to permit the desired communication between the venturi 62 andthe air inlet 54 and opening 56 are provided between the caps 44 and 46and outer flanges 64 and 70.

The outer flange 64 of the upper venturi portion 78 has an annularstepdown shoulder 94 which cooperates with an annular recess 96 in theupper portion 78 of the housing 40 to position it therewith. The innerflange 66 of the venturi upper portion 78 forms upper wall of the middlewater compartment 74. correspondingly, the outer flange 70 of the lowerventuri portion 84 rests upon the lower gasket 92 to position suchportion within the housing 40. The inner flange 68 of the venturi lowerportion 84 forms the bottom wall of the middle compartment 74.

Such flange 68 also cooperates with an annular stop ring 98 welded tothe inner housing wall of the middle compartment 74 to provide a throatslot 88 of adjustable height. As shown in FIG. 2 an annular gage plate100 is positioned between the lower inner flange 68 and stop ring 98 toprovide a throat slot 88 of maximum height. Such height can be decreasedby removing the gage plate 100 and positioning another gasket 92 betweenthe bottom cap 46 and outer flange 70 so that the inner flange 68 abutsthe ring 98.

In practice activated water is continually fed through the water inlet52 into the middle compartment 74 and across the slot 88 forming acontinually flowing sheet of water thereacross. At the same time, airunder pressure is fed through the air inlet 54 into the convergingsection of the venturi 62 which forms an air stream and increases thelinear velocity thereof. The upper segment 82 of the throat increasesthe linear velocity of the air stream to effect an ultrasonic sound wavewhich, together with the airstream, drives through the sheet of waterflowing across the throat slot 88 and continually breaks it up into finedroplets with vibrating surfaces. The commingled air under pressure andthe fine water droplets are then passed through the lower segment 86 ofthe throat to further increase the velocity of the air carrying dropletsbefore being passed into the diverging section 90. In section the waterdroplets and air under pressure are expanded in a controlled manner tothe opening 56 and downwardly flared into stack passage 16 as ultrasonicgenerated fog.

For large quantities of fog, the generator 34 can typically include aventuri 78 with a converging section having an inlet diameter of 1.25inches and an angle of convergence of about 45. The throat of suchventuri is 0.3125 inch in diameter and the throat slot forms an openingof 0.025 inch in height. Such venturi also includes a diverging sectionhaving an angle of divergence of 45. Air under pressure, such as poundsper square inch, is delivered to the venturi by an air supply nipple 54having a nominal diameter of 0.5 inch. correspondingly, the water issupplied to the chamber 74 by a water supply nipple also having anominal diameter of 0.5 inch. The intensity of the sound wave generatedby the venturi typically have an intensity of about decibels and afrequency of greater than 15 kilocycles. The fog generated by suchventuri comprises water droplets which are typically from about l micronto 100 microns in size.

With the venturi type of fog generators 34 just described substantiallygreater quantities of ultrasonically generated fog are now possible forscrubbing flue streams with greater effectiveness than heretoforepossible with conventional water sprayers.

Upon immergence from the ultrasonically dispensed fog of zone A theupwardly flowing flue stream moves into zone B, as shown in FIG. 1,still containing fine carbon particles and substantial quantities ofcarbon and sulphur gases. Within zone B is a centrally positionedfrequency-modulated ultrasonic fog generator 102 suspended above thegenerators 34 of zone A, and three umbrella-type water sprayers 104suspended above generator 102.

The frequency modulated ultrasonic fog generator 102 laterally anduniformly dispenses fog across zone B composed of a range of controlledfine sized, vibrating, chemically activated water droplets for maximumwetting, absorbing and agglomeration of the range of submicron andmicron solid particles. By providing fog having water droplets of arange of controlled fine sizes removal of not only the larger particlesbut the smaller submicron size particles is accomplished, because thesmaller water droplets wet, absorb and agglomerate the submicron sizeparticles while the larger water droplets serve the same function forthe large particles.

Each of the water sprayers 104 positioned above the generator 102 is fedactivated water from conduit 30 and from feed conduit 105, and projectsan umbrella of downwardly flowing water droplets which in combinationprovide ,a uniform curtain of downwardly descending water dropletsacross the stack passage 16 complimenting the previous actions of thegenerators 34 and 102 in removing contaminant from the upwardly flowingflue stream. The water droplets from the sprayers 104 absorb gaseouscontaminants and agglomerate solid contaminants which are still carriedby the flue stream ascending through the water curtain. Hollow conenozzles that employ centrifugal force to break water into droplets canbe used-for such sprayers 104.. Where pollution of the flue stream isnot too great, the water droplets generated in zone B may also besufficient to perform the scrubbing action in zone A as they descendtherethrough. In such instance, the generators 34 need not be used.

As shown in FIG. 5, the frequency-modulated ultrasonic fog generator 102includes a sound generator 106 which laterally generates sound ofvariable frequency together with discharging air under pressure. At thesame time a water feed 108 defining an orifice 1 with the soundgenerator 102 produces an annular stream of water through which thesound and air under pressure move breaking it into fine vibratingdroplets and carrying such droplets in the form of fog across zone B. Byvarying the frequency of the sound generator 102 the variable generatedsound waves break the water droplets into a range of sizes best suitedfor removing the different sizes of solid particles within the fluestream.

As shown in FIGS. 3-5, the sound generator includes a cup 112 having abase 114, and an upwardly extending cylindrical.

wall 1 16 threaded at the lip 118 for securing a correspondinglythreaded closure cap 120. Mounted atop the cup 112 on the closure cap120 is a variable-speed motor 122 and a protective cylindrical shroud124. The motor 122 is secured to the cap 120 by opposing brackets 126depending from and fastened at one end to the motor 122 by means ofscrews 128 and fastened at the other end to opposing horizontal legs 130of L-shaped mountings 132 by screws 134 that extend through abutting legand bracket portions into threaded taps 136 in the cap 120.correspondingly, the shroud 124 is connected to and maintained adistance above the cap 120 by screws 138 which extend through the lowerportion of the shroud wall and which are threaded through threaded hole140 in the vertical legs of the L-shaped mountings 132.

The motor 122 has a depending drive shaft 144 connected to a coupling146 positioned below the motor 122 and within the shroud 124. Secured toand depending from the other end of the coupling 146 is a shaft 148 anda sound generating ring 150 rotatably and slidably mounted within thelower portion of the cup 112. The ring 150 includes four spokes 152secured at one end to the ring 152 and at the other end to a hub 154centrally offset above the ring 150. The shaft 148 is extendable throughand is secured to the hub 154 by means of a setscrew 156. The positionof the ring within the cup 112 is adjustable because the shaft 148 canbe secured in the hub 154 at varying shaft heights.

The ring 150 also includes a plurality of air sound generating passage158 which extend therethrough and which, as best shown in FIGS. 5 and 6,are in the form of rectangular slots. It is to be understood that suchair passages can be of other sound-generating shapes, such as squares orcircles.

Extending about the lower portion of the cup wall 116 is an annulargroove 160 recessed inwardly from the outer surface from the cup 112.Extending through the base of the groove 160 are a plurality of holes162 spaced apart from one another and adapted to communicate with therotated slots 158 of the ring 150 for generating sound. Like the airpassages 158, the holes 162 can be formed of various shapes. In theillustrative embodiment, such holes 162 are circular with a diameterabout equal to the height of the groove base and the width of therectangular slots 158 while being about one-half the height thereof. Asshown in FIG. 5, the ring 150 is positioned within the lower portion ofthe cup 112 so that the holes 162 intermittently communicate with thecentral portion of theslots 158 as the ring 150 is rotated.

For feeding air under pressure into the cup 112, a feed conduit 164 isconnected to the supply conduit 32 as shown in FIG. 1, and man air inletnipple'l66 which extends from and is welded to the cup wall 116 about adrilled hole 167 having a diameter equal to the inside diameter of thenipple 166. The drilled hole 167 is positioned in the central portion ofthe cup wall above the ring 150, as shown in FIG. 5. An L-shaped conduit168 having one end in the bore 166 and the other end ex-' tendingthrough and secured to the closure cap 120 so as to be positionedimmediately below the motor 122 siphons some of the air under pressureto cool the motor 122.

The cup 112 also includes an annular bevel 170 which serves as onesurface of the water feed orifice 110. The bevel 170 is inwardlyinclined from the lower edge of the groove 160 to and contiguous withthe lower peripheral portion of the annular groove 160 which defines theholes 162.

For supplying water to the feed orifice 110, the feed 108 includes acircular baseplate 172 having a hole 174 therethrough offset from thecenter thereof. Welded to the plate 172 about the hole 174 is a waterinlet nipple 176 which is also connected to the water supply conduit 30via feed conduit 178, as shownin FIG; 1. Extending upwardly from thebaseplate 172 about the cup wall 116 is an annular sleeve 180 with aninturned rim 182 forming a water chamber 184. The inner edge 186 of therim 182 serves as the other surface of the orifice 110 by defining anoutwardly inclined bevel spaced from and parallel to the bevel 170.

To maintain the feed 108 and cup 112 in the desired spaced relationship,a support 188 is welded to the bottom of the cup 112 having a threadedstud 190 which extends through a central opening 192 in the baseplate172 to receive a nut 193 adjustably secured to said stud 190. Apregauged washer 191 positioned between underside support 188 and insidesurface of baseplate 172 provides the maximum opening of orifice 110.Such orifice opening can be decreased by adding additional pregaugedwashers to washer 191.

In practice, the motor 122 rotates the ring 150 within the cup so thatthe cup holes 162 are intermittently open to the interior of the cup viathe slots 158. The pressurized airflow from the air conduit 164 andinlet nipple 166 to the cup and through the holes 162 is thereforeintermittently interrupted with the result that sound is generated.which laterally eminates from said holes 162 when communication withthe cup interior is permitted by slots 158.

Simultaneously, a vertical upward annular stream of activated water isprovided from the feed 108 through the orifice 110 about the holes 162,whereupon the laterally generated sound and air pressure issuingtherefrom moves into and through the water stream to break such streaminto fine vibrating water droplets. The fine vibrating droplets are thencarried laterally across zone B by the air under pressure in the form offog.

The frequency of the generated sound relates to the speed of rotation ofthe ring 150 and the number of air passages 158 therethrough. Eachfrequency of generated sound predominantly produces droplets of one sizeso that by providing a range of frequencies droplets of different sizesare laterally carried across zone B. In so doing, the fog containsdroplets of a size best suited to wet, absorb and agglomerate aparticularsized solid particle carried by the flue stream. This isespecially advantageous for removing the fine micron and submicron sizedparticles which have heretofore escaped into the atmosphere.

To produce sound at different frequencies, the variablespeed motor 122rotates the ring 150 at different preselected speeds. In turn, the speedof the motor 122 is controlled by a motor control circuit 200 shown inFIG. 8 which is connected to said motor 122 by wires 194 extendingthrough a grommet 196 secured to the shroud 124 by a lock nut 198 shownin FIG. 5.

The frequency modulation rate of the motor control circuit 200 isachieved with a low frequency oscillator 202, such as a Hartley orColpitts oscillator. The output of this oscillator 202 is used to drivethe voltage at a controlled oscillator 204. A typical voltage-controlledoscillator is the free running multivibrator shown in FIG. 9 anddescribed hereinafter. The output from the voltage-controlled oscillator204, in turn, controls the silicon-controlled rectifier gated voltagecontroller 206 which can be one of the known motor speed controllers.Thepurpose of this controller 206 is to control the average currentthrough the motor armature 208 of the motor 122. Also shown in FIG. 8are the motor shunt field 210 and the DC power supply 212 which areessential for the operation of frequency-modulated ultrasonic generator102.

Since the speed of a DC motor varies with respect to the current throughits armature, the (SCR) controller 206 controls the speed of the ,motor122 which, in turn, controls the frequency of the ultrasonic foggenerator 102. The normal speed of the motor 122 depends on thefree-running frequency of the multivibrator or voltage-controlledoscillator 204, and the rate at which the speed of the motor 122changes, or the rate of the ultrasonic frequency changes, depends on thelow frequency oscillator 202 which modulates the voltagecontrolledoscillator.

Typically the frequency-modulated ultrasonic fog generator 102 of theinvention is supplied with air under pressure, such as 100 pounds persquare inch, from an air inlet nipple having an 0.5-inch nominaldiameter. correspondingly, the water is supplied to the generator 102through a water inlet nipple 176 also having 0.5-inch nominal diameter.The frequency-modulated ultrasonic fog generator of the inventionproduces a sound wave having an intensity greater than 110 decibels anda frequency from about 10 to 30 kilocycles.

From zone B the flue stream moves upwardly into the filtering zone C oflow-flow resistance, of large surface area, of substantial depth, and ofinfinite filtering capacity, wherein all or essentially all of theremaining solid and gaseous contaminants are removed from the fluestream. Upon emergence from zone C greater than 99.99 percent of allsolid contaminants, including carbon particles of micron and submicronsizes, and known carbon and sulphuric gaseous contaminants are removedfrom the flue stream. The purified flue stream then passes through thebalance of the stack 10 to atmosphere.

Within zone C is positioned the filter 300 of the invention whichincludes a frequency-modulated ultrasonic fog generator 304, anelectrical field generator and sound vibrator 310, and an electricvibrator control means 303. 1

Suitably suspended and centrally positioned within the filter 300 is thefrequency-modulated ultrasonic fog generator 304, the structure andfunction of which are the same as previously described for generator 102of zone B. Water and air under I pressure is fed to the generator 304 byfeed conduits 31 and 32 connected to the water and supply conduits 30and 32, respectively. As previously described, lateral emanating soundof preselected varying frequency and air under pressure break up anupwardly moving annular stream of water to produce lateral-moving fogcomposed of chemically activated water droplets of varying sizes. Inthis zone, moreover, the droplets are charged electrically by the fixedpotential of the vibrator 310 which is applied to'water feed conduit 31as will presently be described.

The field generator and vibrator 310 includes a pair of spacedstationary outer, circular, screen-type grids or electrodes 306 and 308suitably supported and positioned across the stack passage 16 so as tobe insulated from the stack 10. Centrally positioned between the grids306 and 308 is a porous, circular, vibrating, sound-generating grid 310having a central ring 312 in which is suspended the fog generator 304.From the ring 312 extends a plurality of radial, rectangularly shapedspokes 314. Connected between each pair of spokes 314 are a plurality ofspaced, arcuate-shaped, coiled springs 316, forming with the springsbetween the other pairs of spokes circular vibrators. For strengthradial coil springs 317 are connected between the outer pairs ofarcuate-shaped springs 316.

The screens 306, 308 and 310 are energized through a transformer318'a'nd the high-voltage bias supply consisting of diodes 320 and322and filtering capacitor 324. The transformer 318 is powered'throughpush-pull transistors 326 and 328 which, in turn, are power driven by avoltage control oscillator circuit.

The frequency modulated power supply includes a unijunction transistor330which is part of a frequency modulation control for sawtoothpulse-generating stage, a pair of NPN transistors 332 and 334 whichoperate as a free-running multivibrating stage, and the transistors 326and 328 which operate as a'power' output stage. The bases of theunijunction transistor 330 are connected to ground and the positivesource of supply through resistors 336 and 338, respectively. The RCcircuit is formed by a resistor 340 and a capacitor 342 connected inseries between the positive source and ground. The emitter of theunijunction transistor 330 is connected to the junction between theresistor 340 and the capacitor 342.

When the potential is applied to the pulse-generating circuit apotential gradually builds up across capacitor 342 and when thispotential reaches the breakdown potential of the transistor thecapacitor discharges through one of the emitter base circuits of thetransistor. As a result, a sawtooth signal is developed across thecapacitor.

The emitters of transistors 332 and 334 in the multivibrator circuit areconnected to ground via resistors 344 and 346, respectively, whereas thecollectors are connected to the positive source through resistors 348and 350. Capacitors 352 and 354 provide the cross coupling networks:capacitor 352 being connected between the collector and transistor 334and the base transistor 332, and capacitor 354 being connected betweenthe collector of transistor 332 and the base of transistor 334. Thebases of transistors 332 and 334 are connected to ground respectivelythrough resistors 356 and 358 and are also connected to one anotherthrough series resistors 360 and 362. The conductor 364 couples thejunction of resistor 340 and capacitor 342 to the junction of theresistors 360 and 362.

The free running multivibrator circuit including transistors 332 and 334operates with the transistors alternately becoming conductive. Thefrequency of the oscillator is controlled by the RC coupling network352, 354, 356 and 358 in conjunctionwith'the synchronizing signal fromthe sawtooth pulse generator that supplied via conductor 364.

The collectors of amplifying transistors 326 and 328 are connected toopposite'ends of a primary winding 366 of transformer 318, and. theemitters of these transistors are connected to ground. The base oftransistor 326 is coupled to the emitter of transistor 334 and the baseof transistor 328 is connected to the emitter of transistor 332. Ahighvoltage positive source is connected to the center tap of primarywinding 366.

Transistors 326 and 328 are periodically, and alternatively, driven intothe conductive states as determined by the associated drivingtransistors 332 and 334 in the multivibrator circuit. As a result, asquare wave, alternating signal is developed across the primary windinghaving a fundamental frequency as determined by the RC circuitassociated with unijunction transistor 330, and the free runningfrequency of the multivibrator.

Transformer 318 is a high-voltage step-up transformer capable ofdeveloping a 200,000 peak-to-peak voltage across the transformersecondary winding 368.

One end of secondary winding 368 is connected to stationary grid 306 andthe other end of the winding is connected to stationary grid 308. Thecenter vibrating grid 310 is coupled to the center tap of the secondarywinding 368 through a capacitor 324. The capacitor 324 is charged by thepair of diodes 320 and 322 with the cathodes and the diodes connected tothe ends of secondary winding 368 and the anodes and the diodesconnected to a common junction 370 between capacitor 324 and thevibrating grid 310. Because of the high voltages appearing across thesecondary winding of the trans former diodes 320 and 322 would normallyconsist of a series string of diodes including a sufficient number ofdiodes having a combined peak inverse voltage rate exceeding the peaksecondary winding and the capacitor 324 voltage. For convenience,junction 370 is grounded so that their connections can be made to thevibrating grid without providing high-voltage insulation.

Diodes 320 and 322 act as a rectifier circuit which develop ahigh-voltage potential across capacitor 324. This potential is positiveat the center tap and negative on the other plate of the capacitorhaving a voltage corresponding to the peak-to-peak potential of one-halfof the secondary winding. The potentials developed on the outer gridswith respect to the center grid, (ground) are as shown in FIG. 10. Thepotentials e and 2 represent the potentials applied to grids 306 and 308with respect to the center or vibrating grid 310, whereas the potential2 represents the potential which appears across capacitor 324. It shouldbe noted that by providing an offce'nter bias to the vibrating grid withrespect to the outer stationary grids, the maximum peak-to-peaksecondary voltage can be developed between vibrating grid and the outergrids. Thus the circuit including capacitor 324 and diodes 320 and 322make it possible to develop twice the potential difference betweenadjacent grids then would otherwise be possible if the vibrating gridwere connected directly to the center tap of secondary winding 368.

In practice, the frequency-modulated ultrasonic generator 304 laterallyand continuously discharges a uniform blanket of fog across the filter300 immediately above the intermediate grid 310. As previously describedthe fog is composed of droplets having vibrating surfaces and being of arange of micron size best suited to remove the solid contaminant stillcarried by the flue stream. At the same time, the high-voltage,alternating potential applied to the outer grids 306 and 308 produces avery strong electrical field vertically across the laterally moving fogto cause three-dimensional oscillation of the water droplets. Thisoscillatory motion is further accentuated by the sound wave generated bythe vibrating coiled springs of the intermediate grid 310 alternatelyattracted, in a The effectiveness of the overall process hereindescribed is dramatically shown by the following tabulation which setsforth the effectiveness of each zone of the process:

As can be seen from the tabulation more than 99.99 percent of all solidcontaminants irrespective of size and a like percent of gaseouscontaminants are removed from the flue stream by the present invention.

As described at the outset of the illustrative embodiment activatedwater collected at the stack base 24 is drained through conduit 26 toreservoir 28, separated from the collected solid particles and recycledback into the process. For this purpose reservoir 28 has an inletsection 400 open to the drain conduit 26, an intermediate weir section402, and an outlet section 404 from which the cleansed activated wateris recycled back into the process.

The inlet section 400 has a drain 405 at the base thereof for removingcollected solid particles which fall by gravity through the collectedwater to the base of such section 400. To prevent flow of solidparticles to the outlet section 404, the intermediate weir section 402includes a pair of spaced plates 406 and 408. Plate 406 depends from thetop of and is of a height less than the height of the reservoir 28.Correspondingly, plate 408 extends from the bottom of the reservoir 28and is also of a height less than the height of the reservoir.

Mounted atop the reservoir 28 is a vertical suction pump 410 havinganintake strainer 412 depending into the outlet section 404. The pumpoutlet is, in turn, connected to the water supply conduit 30 viainterconnecting feed conduit 414. Shutoff valve 416 and strainer 418 areprovided in the conduit 414 as a further flow and cleansing control ofactivated water.

, Fresh makeup water is added to the reservoir section 404 as requiredfrom a makeup water source connected to the outlet section 404 viaconduit 420. To control the flow of fluid to the section 404, asolenoid-operated valve 422 is connected in the conduit 420. Thesolenoid of the valve 422 is actuated by a water levelindicator 424which floats upon the water in the outlet section 404. When the levelindicator 424 is in the phantom position shown in FIG. 1, the solenoidopens the valve 422 to permit the flow of makeup water into section 404.As the level indicator 424 rises with the increase of water and reachesthe position shown byv the solid lines, the solenoid valve 422 is closedto stop flow of the makeup water.

As also shown in FIG. 1, the outlet section 404 is provided with a drain426 in which there is a shutoff valve 428. Normally the valve 422 isclosed but in case of excess fluid in the outlet section 404, the valve428 is opened to restore a suitable level within the reservoir 28.

The purifying process described herein is of low-flow resistance.However, extreme pollution conditions may require particularly heavyconcentration of water droplets within the stack passage 16. To insureproper flue flow at all times, a motor-operated induction fan 430 isconnected into the lower end of the stack 10. Operation of the fan 430is controlled by a flue velociometer 432 attached to the inner wall ofthe stack 10 above zone C as shown in FIG. 1. When the flue flow fallsbelow the desired level, the velociometer 432 causes the motor-operatedfan 430 to introduce fresh air into the flue stream until the flue flowonce again reaches the desired level. An airflow indicator and alarm 434is also connected to the velociometer 432 to provide a visual andaudible warning to an operator.

To vary the amount of water droplets generated within the stack relativeto the smoke density and temperature of the flue stream there isprovided a pair of solenoid-operated valves 436 and 438 connected intothe water feed conduit 36 and 105 for the generators 34 and sprayers104, respectively, controlled by computer system 440. The valves 436 and438 are normally preset to permit sufficient water flow therethrough forthe removal of normal contaminant quantities carried by the flue stream.Whenever the quantities of contaminants are increased, the valves 436and 438 are opened further by the system 440 to allow additionalquantities of water to flow therethrough for producing an increasedconcentration of water droplets.

The computer control system 440 for controlling the water dispensedthrough the water sprayers I04 and fog sprayers 34 is shown in greaterdetail in FIG. 11. The computer control includes two independentlyoperating control loops, one control loop operating to increase thewater flow as the smoke density increases as determined by a detector441, and the other control loop operates to increase the water flow asthe temperature increases as determined by a temperature detector 442.

Temperature detector 442 can be any conventional temperature-measuringdevice, such as a temperature-responsive resistance or a thermocouple,which provides an electrical signal proportional to temperature. Thesmoke density detector includes a modulated light source 444 whichprovides a modulated light beam which crosses the stack passage 16 andis then reflected off a mirror 443 to a photocell detector 441. Thus, asthe smoke density increases the amount of light received by detector 441decreases and therefore the magnitude of the electrical signal providedby the detector decreases proportionally.

Referring to FIG. 11 it should be noted that the controlled circuitryincludes two independent control loops. As previously described inconnection with FIG. 1, the modulated light source 444 provides a lightbeam which passes through the stack passage 16 and is detected by alight sensor 441. The electrical signal provided by the light sensor isamplified in an amplifier 445 and passes through a signal conditioner446 which is designed to remove extraneous noise from the signal. Lightbeam detectors are inherently noisy and it is therefore desirable tomodulate the light beam by means of a modulator 447. The modulatoramplitude modulates the light beam as provided by the source 444 andalso provides a signal to a signal demodulator 448 so that allextraneous noise can be eliminated from the electrical signal.

A reference signal source 449 provides a controlled electrical signalcorresponding to the desired smoke density in the stack passage 16. Thereference signal is compared with the demodulated signal in a levelcomparator circuit 450 so that the level comparator circuit provides anoutlet signal when the demodulated signal deviates from the value of thereference signal.

The output signal from the level comparator passes through an isolatingOR circuit 451 and an amplifier 452 to in turn control the valveactuator 453 connected to valves 436 and 438 and thereby control thewater quantity supply to the stack passage 16. Thus, whenever the smokedensity exceeds the predetermined value determined by the referencesignal, actuator 453 operates the solenoids to further open the valves436 and 438 and thereby increase the water supply to the stack passage.Since the quantity of water injected into the stack passage affects thesmoke density, and this effect appears in the signal provided by thelight sensor, the system operates in a closed loop fashion to controlsmoke density.

The other control loop of the computer control circuit includes thetemperature sensor 442 which provides an electrical signal proportionalto temperature in the stack passage. This electrical signal is amplifiedin an amplifier 454 and supplied to the electrical comparator circuit455. The reference temperature source 456 provides an electrical signaldetermined increase with the desired stack temperature. The referencesignal and the signal from the temperature sensor are compared incomparator circuit 455 which provides an electrical output signal to ORcircuit 451 whenever the stack temperature exceeds the desired value.The electrical signal from the comparator passes through the OR circuitand amplifler 452 to control the water quantity actuator 453 aspreviously explained. OR circuit 451 provides an isolating function sothat the comparators 450 and 455 will not interfere with one another.

Increased water flow into the stack passage tends to decrease thetemperature and this effect is sensed by the temperature sensor 442. Asa result, the temperature control circuit also operates in a closed loopfashion.

Indicators and alarms diagrammatically illustrated and designated inFIG. II as A are'connected to the computer control system 440 to givevisual and audible indications of the temperature level at thetemperature detector 442 and the smoke density at the smoke detectorpositioned above zone C.

Thus, the method of and apparatus for the present invention are flexibleand ready to meet changing conditions of the polluted gaseous stream.

While this invention has been particularly described in the illustrativeembodiment with respect to removing contaminants from a flue stream of asteam generated furnace, it is to be understood that this invention canbe used to remove contaminants from polluted gases generated from otherprocesses such as in steel mills, chemical process plants,sulphur-manufacturing plants, metal-processing plants andfood-processing plants.

The invention in its broader aspects therefore is not limited to theillustrative embodiment but departures can be made therefrom within thescope of the accompanying claims without departing from the principlesof the invention and without sacrificing its chief advantages.

What is claimed is:

1. An ultrasonic fog generator comprising a housing member, a venturimember positioned within said housing member, said venturi memberincluding a converging section at the other end thereof, a divergingsection at the other end thereof, and a restricted throat sectionconnecting said converging and diverging sections to one another, saidrestricted throat section having a slot extending therethrough forsubstantially the entire width thereof and in a plane substantiallytransverse to the axis thereof, means for feeding water into saidhousing adjacent the throat section and through said slot presenttherein to form a continuously flowing thin sheet of water across theentire width of said throat section, and means for feeding gas underpressure into said converging section wherein the gas is formed into astream and thereafter fed into the throat section to increase the linearvelocity of said gas stream to produce a sound wave in said throatsection which, together with said gas under pressure, moves through saidsheet of water flowing across the width of said throat section therebycontinually breaking said sheet of water into fine water droplets havingvibrating surfaces, said commingled gas under pressure and the finewater droplets upon reaching said diverging section being expandedtherein and passing therefrom as an ultrasonically generated fog.

2. The ultrasonic fog generator of claim 1 wherein said throat sectionhas two segments spaced apart to form the slot therethrough.

3. The ultrasonic fog generator of claim 2 wherein said throat segmentsare adjustably spaced apart.

4. The method of forming ultrasonic fog which comprises passing gasunder pressure into a first zone, increasing the linear velocity of saidgas stream by passing said gas from said first zone into a second zonehaving a restricted cross-sectional area to produce a sound wave withinsaid second zone, forming a continuous sheet of water across the widthof said second zone, moving the sound wave and gas under pressurethrough said formed sheet of water to continually break said sheet ofwater into fine water droplets having vibrating surfaces, passing saidwater droplets having vibrating surfaces into an expansion third zone toproduce an ultrasonically generated fog.

2. The ultrasonic fog generator of claim 1 wherein said throat sectionhas two segments spaced apart to form the slot therethrough.
 3. Theultrasonic fog generator of claim 2 wherein said throat segments areadjustably spaced apart.
 4. The method of forming ultrasonic fog whichcomprises passing gas under pressure into a first zone, increasing thelinear velocity of said gas stream by passing said gas from said firstzone into a second zone having a restricted cross-sectional area toproduce a sound wave within said second zone, forming a continuous sheetof water across the width of said second zone, moving the sound wave andgas under pressure through said formed sheet of water to continuallybreak said sheet of water into fine water droplets having vibratIngsurfaces, passing said water droplets having vibrating surfaces into anexpansion third zone to produce an ultrasonically generated fog.